1. Field of the Invention
The present invention relates to an optical device for a camera device. More particularly the present invention relates to a device that is capable of suppressing the reflection of incident optical signals.
2. Description of the Related Art
In general, a camera device has a lens array and converts incident optical signals into electrical signals, which are processed into desired images for display or storage. Portable terminals are equipped with such a camera for multi-function service. Particularly, mobile telephones are often equipped with such a camera. When mounted on a portable terminal, however, the camera has a limited size. This is an obstacle to improving the resolution.
FIG. 1 shows an example construction for processing image signals photographed by a camera device for display or storage.
Referring to FIG. 1, an optical unit 10 has a lens array and generates optical signals of photographed images. An image sensor unit 20 (such as a CMOS image sensor) converts the photographed optical signals into electrical signals. An image processing unit 30 processes the image signals output from the image sensor unit 20. The image data processed by the image processing unit 30 is output to a display unit 40 to be displayed or to a memory 50 to be saved.
Factors affecting the resolution of images in a camera device configured as shown in FIG. 1 include non-uniformity of the lenses constituting the optical unit 10, a flare phenomenon of the optical unit 10, a halation phenomenon of the image sensor unit 20, and white clip, linearity, dark current, and noise of the image processing unit 30. The most critical factor among them is related to the optical unit 10. If the image resolution degrades in the optical unit 10, the following image processing unit 30 has a limitation on its ability for improving images. Therefore, problems related to the optical unit 10 must be solved first.
FIG. 2 shows a conventional construction of the optical unit 10 and the image sensor unit 20 shown in FIG. 1.
Referring to FIG. 2, a window glass 110 is positioned in front of a lens array 130 and prevents alien substances from contacting the lens array 130. A barrel 120 retains the lenses of the lens array 130, and the interior of the barrel 120 has a structure adapted to retain each lens of the lens array 130. The lens array 130 performs the function of focusing incident optical signals of photographed objects. The lens array 130 may include a focusing lens, a variator lens, a compensator lens, an elector lens, and a relay lens. Each lens may have an array of a number of lenses to perform each corresponding function. When used in a small portable terminal, the lens array 130 may include only a focusing lens. The focusing lens performs the function of forming the same focus regardless of the focal length.
An infrared filter 141 performs the function of interrupting infrared rays from incident optical signals. The infrared filter 141 may be positioned on the front or rear of the window glass 110. An image sensor 143 is also provided at the rear of the window glass 110.
FIGS. 3a and 3b show the internal construction of an image sensor 143 of FIG. 2. The image sensor 143 as shown in FIGS. 3a and 3b, includes a faceplate 161, a micro-lens 163, and a photocell 165. The faceplate 161 is positioned between the micro-lens 163 and the photocell 165 as a medium for connecting the micro-lens 163 and the photocell 165 to each other. The micro-lens 163 performs the function of focusing optical signals which have passed through the infrared filter 141 to the photocell 165. After passing through the micro-lens 163, the optical signals become a single pixel. The photocell 165 performs the function of converting optical signals output from the micro-lens 163 into electrical signals. The infrared filter 141, faceplate 161, micro-lens 163, and photocell 165 can constitute the image sensor unit 20 shown in FIG. 1.
The optical unit 10 and the image sensor unit 20 perform the functions of optically processing incident optical signals and converting the processed signals into electrical signals. Non-uniform coatings of each lens array 130 of the optical unit 10 and reflection (e.g., flare) of incident optical signals may generate unwanted characteristics of optical signals, and a halation of the image sensor unit 20 may also vary the characteristics of optical signals. As used herein, a flare refers to an optical reflection between the lenses of the optical unit 10 and a halation refers to an optical dispersion of the faceplate 161.
The causes of the quality degradation of optical signals photographed by the optical unit 10 will now be described in greater detail. Optical signals incident from the optical unit 10 are reflected and create unwanted optical signals due to substantially three reasons, including the structure of the window glass 110 and the barrel 120, the lens array 130, and the internal structure of the barrel 120.
Firstly, the window glass 110 is spaced at a predetermined distance X from the barrel 120 as shown in FIG. 2. Specifically, the window glass 110 is positioned in front of the barrel 120 retaining the lens array 130 with a spacing therebetween, in order to prevent alien substances from contacting the lens array 130. The distance X between the window glass 110 and the front part of the barrel 120 creates a reflection wave of an incident optical signal R1. Specifically, as the incident optical signal R1 passes through the window glass 110, it is reflected by the front surface of the barrel 120 and is incident on the window glass 110. The optical signal R1 is again reflected by the surface of the window glass 110 and is incident on the lens array 130. As a result, the unwanted optical signal R1 incident on the lens array 130 is optically processed and degrades the image resolution.
Secondly, non-uniform coatings of the lens array 130 may cause incident optical signals to be reflected. Specifically, the lens array 130 includes a number of lenses. The lens array 130 shown in FIG. 2 may be made up of a focusing lens including two glass lenses and two plastic lenses. Non-uniform coatings of the lenses constituting the lens array 130 may vary the transmittance, and the lenses may generate an unwanted reflection optical signal R2.
Thirdly, optical signals reflected by the lens array 130 may be reflected within the barrel 120 and incident on the lens array 130 again. Specifically, an unwanted optical signal R3 may be generated due to reflection within the barrel 120 for retaining each lens of the lens array 130.
As described above, the non-uniform coatings of lenses constituting the optical unit 10, internal structure of the barrel 120, and spacing between the barrel 120 and the window glass 110, can each alone or in combination generate unwanted optical signals R1-R3, which may result in a flare phenomenon in the imaging system of the optical unit 10. The unwanted optical signals R1-R3 also degrade the resolution of images finally processed.
The image sensor unit 20 may also generate unwanted reflection waves.
FIG. 3a shows the path of incident optical signals between the optical unit 10 and the image sensor unit 20, and FIG. 3b shows the structure of the micro-lens 163 and the photocell 165 shown in FIG. 3a. After passing through the lens array 130, optical signals are incident on the micro-lens 163 via the infrared filter 141. After being focused by the micro-lens 163, the optical signals are incident on the corresponding photocell 165 and are converted into electrical signals. The micro-lens 163 and the photocell 165 constitute a pair, the number of which corresponds to the number of pixels necessary for photographing with the camera. For example, a camera having a million pixels needs a million micro-lenses 163 and a million photocells 165.
However, the image sensor unit 20 is vulnerable to a halation phenomenon caused by the faceplate 161 and the micro-lens 163 as shown in FIGS. 4a and 4b. Specifically, reflection within the faceplate 161 generates a halo as shown in FIG. 4a and irregular reflection caused by the micro-lens 163 generates a halo as shown in FIG. 4b. 
As described above, the flare phenomenon occurring in the optical unit 10 and the halation phenomenon occurring in the image sensor unit 20 are major factors degrading the contrast, resolution, and color density of processed images. Such degradation of images place a limitation on improving images with the following image processing unit 30.
Accordingly, a need exists for a system and method for suppressing reflection optical signals occurring in an optical system of a camera.